I've created a new VM from using the Quick Create function in Hyper-V on windows 10.

Once the VM is setup (I've picked language settings, created a password etc) I then tried to install Visual Studio Code and got the following error message:
Unable to install "Visual Studio Code": too early for operation, device not yet seeded or device model not acknowledged.

5 - messing around with /var/lib/snapd/seed/seed.yaml

I tried re-ordering the gtk-common-themes part and also removing the gnome-calculator part (rebooting after each change), this appeared to make no difference. The snap tasks --last=seed command still showed it getting stuck on the gnome-calculator task.

6 - headbutting the keyboard

I felt better but the issue persisted.

7 - using a non-quick start image

I downloaded a Ubuntu 18.04.2 ISO and used that. THIS WORKED (as in I could install Visual Studio Code and the snap commands looked healthy). However, it doesn't have all the nice hyper-v stuff so the screen res sucked, no copy and paste, mouse was very laggy etc...

I could install the various bits to make this image more hyper-v friendly but I have a feeling I'll never get as slick as the official one. If I can fix the snap on this one I think I'll end up with the best UX.

8 - THIS WORKS. messing around with /var/lib/snapd/seed/seed.yaml part 2

I removed a bunch of stuff from my /var/lib/snapd/seed/seed.yaml so it now looks like this:

I can confirm that this helped, however what it does is it removes the packages not only from yaml, but also from system (they are not visible anymore)... What I did is simply reinstalled them back (some of them, the rest got reinstalled automatically)
– Stefan JarinaMay 18 at 16:49

Same issue remains on Hyper V Ubuntu 19.04 image. Problem solved with your solution above! It took be a while to find your post though as I was searching / googling with 19.04. Maybe you can add this version in question title for better index search.
– BoudJun 23 at 2:34